Target Radial Velocity Research Articles

An Adaptive False Target Suppression and Radial Velocity Estimation Method of Moving Targets Based on Image-Domain for High-Resolution and Wide-Swath SAR

An Adaptive False Target Suppression and Radial Velocity Estimation Method of Moving Targets Based on Image-Domain for High-Resolution and Wide-Swath SAR

A real‐time fine echo generation method of extended false target with radially high‐speed moving

The false-target echo generation to Inverse Synthetic Aperture Radar (ISAR) is significant in jamming the enemy ISAR and promoting ISAR development. Generally, it requires false-target echo coherent with the radar, real time and fine. However, conventional methods, such as digital image synthesizer (DIS), cannot meet those requirements. Moreover, existing methods do not consider the target's radial moving. To meet those demands, we propose an improved method in this study. We equivalently model echo formation as the synthesizer of two independent parts: (1) echo of remote target with radial moving and (2) echo of nearby extended target. In part one, accuracy is improved by utilising the Inner Pulse Motion (IPM) model and complexity is simplified by deducing it as a frequency offset modulation. In part two, the fine extended target echo is constructed by using convolution filtering whose resources consumption can be greatly reduced by separating it into an offline stage and a real-time stage. Our method is verified by algorithm simulations and actual experiments. The results indicate that it can build the fine false-target echo in real-time and can adapt to the target's radial velocity, different resolution and size. Compared with the conventional DIS method, our method reduces the computational complexity significantly and has more comprehensive functions.

Method for long-term coherent-noncoherent signal accumulation with non-zero higher derivatives range to radar target

A method of long-term combined accumulation of the reflected signal is justified, which provides for its division into disjoint subsets, coherent accumulation in subsets using one of the fast algorithms and subsequent incoherent accumulation of the squares of the modules of the results of processing the subsets. A distinctive method’s feature is the use with incoherent accumulation of maxima of the squares of the moduli of the coherent processing results, that are selected from the range / radial velocity regions in accordance with a given hypothesis about the minimum and maximum values of the target radial velocity and the radial acceleration detection channel setting.The efficiency of the method was confirmed by simulation modeling. Using the theories of ordinal statistics and the method of moments, a method for calculating the probability of correct detection is developed. Estimates of processing losses are made in comparison with coherent and incoherent accumulation algorithms for a signal reflected from a point target, for the case when there is no range and frequency migration. Estimates for the required number of receiver channels are given.

Digital Detection and Tracking of Tiny Migratory Insects Using Vertical-Looking Radar and Ascent and Descent Rate Observation

Vertical-looking radar (VLR) is a significant milestone in the development of insect radars with the capability of detecting the behavior of migratory insects and their biological parameters. In current VLRs, high-speed continuous sampling and long-time integration can barely be performed simultaneously, leading to a low detection probability for tiny insects (weight < 10 mg). Based on the large amount of data acquired by our developed high-range resolution insect radar, the insect echo signals and vertical motion characteristics are initially analyzed and demonstrate that the linear-motion mode is dominant in insect migration; also, the echo signal power of most insects follows the gamma distribution. Based on these characteristics, a long-time integration and detection method for detecting migratory insects, especially tiny targets from echo signals that often dip below the noise level, is proposed. The radial target velocity is also measured as one of the output parameters. The theoretical derivation and optimal choice of detection thresholds are also presented. Simulation and experimental results demonstrate that the proposed method exhibits better insect detection performance and effectively increases the detection range compared with conventional methods. In addition, the measured target velocity can be directly applied to current continuous-sampling VLRs for the ascent and descent rate analysis. Many typical insect migration phenomena have been detected effectively utilizing our developed VLR, and the measured ascent and descent rates of insects agree well with typical take-off, cruising, and landing behaviors. This is the first reported successful VLR application on take-off and landing behaviors of migratory tiny and dense insects.

Vessel Velocity Estimation and Tracking From Doppler Echoes of T/R-R Composite Compact HFSWR

Vessel speed and heading are two important kinematic parameters describing its state of motion. However, due to low spatial resolution of a compact high-frequency surface wave radar (HFSWR), vessel speed and heading cannot always be accurately estimated. Since HFSWR can measure vessel Doppler velocity with relatively high accuracy, it is possible to estimate a vessel's vector velocity based on two Doppler velocities measured along two different directions. In this article, a newly developed T/R-R composite compact HFSWR system is introduced, and a corresponding vessel velocity estimation method which employs a target's radial velocity and elliptical velocity, respectively, measured by the monostatic (T/R) and bistatic (T-R) settings is proposed. First, monostatic and bistatic tracks are independently generated using a multitarget tracking algorithm. Then, the obtained monostatic and bistatic tracks are matched using a track-to-track association method to determine the track pair belonging to each target. Subsequently, the associated track pairs are combined to produce fused tracks for improving positioning accuracy. Finally, vessel vector velocity is estimated based on the radial and elliptical velocities as well as the fused target position. Comparisons of vector velocity estimation results from radar field data with corresponding automatic identification system data demonstrate that the average root-mean-square-errors of the estimated speed and heading are 0.48 km/h and 3.9 $^{\circ }$ , respectively, which meets the practical requirements of a maritime surveillance system. Moreover, the velocity estimation error is analyzed via theoretical derivation and experimental verification. The proposed method shows good potential in further improving the tracking accuracy.

A Machine Learning-Based Approach for Auto-Detection and Localization of Targets in Underwater Acoustic Array Networks

The localization and tracking of underwater objects have many applications. In a proactive underwater sensor array, some nodes will periodically broadcast linear frequency modulated (LFM) signals, which will hit the targets, get reflected and received by the other nodes. Depending on the target's position and velocity, the received signals will also be LFM signals of different frequencies and frequency rates. We can use the Fractional Fourier Transform (FrFT) to analyze the received signal's spectrum and find the peak. Based on the location of the peak, the target's distance and radial velocity can be estimated. However, the accuracy is highly dependent on the sampling interval of the spectrum. Smaller sampling interval leads to higher accuracy but also induces considerable complexity. To overcome this issue, we propose a machine learning-based approach to automatically detect the existence of the target, and roughly estimate the peak's location if targets exist. Then over-sampling can be conducted for a small area around the peak, leading to improved accuracy and reduced complexity. The idea is based on the following observation: if a target exists, we will be able to observe an “X” pattern on the spectrum. Extensive simulations are conducted to verify the effectiveness of the proposed architecture.

Long-time coherent integration and motion parameters estimation of radar moving target with unknown entry/departure time based on SAF-WLVT

In practical application, the time when the maneuvering targets enter and leave the radar coverage observation is usually unknown, which will seriously deteriorate the performance of coherent integration and target detection. To solve this problem, we propose a method based on the symmetric autocorrelation function and the proposed window Lv's transform (SAF-WLVT) for coherent integration and motion parameters estimation of maneuvering target, involving the range migration (RM) and Doppler frequency migration (DFM). Firstly, the SAF is utilized to correct the linear RM induced by target's radial velocity and range curvature caused by target's radial acceleration simultaneously. Then, the proposed WLVT is applied to eliminate the residual DFM caused by the target's radial acceleration, accumulate the target energy without introducing excess noise energy, and obtain the baseband velocity and acceleration estimations. Finally, the Doppler ambiguity number is estimated by matched filtering and 1-D parameter searching, and then the target's radial velocity is obtained. The proposed method has low computational complexity, and possesses favorable performance of target detection and parameter estimation in the high signal to noise (SNR) environment. The mathematical analysis and simulation results demonstrate the effectiveness of the proposed method.

Road-Aided Along-Track Baseline Estimation in a Multichannel SAR-GMTI System

In this letter, a novel method is proposed to estimate the along-track baseline for a multichannel synthetic aperture radar (SAR) system, intended for ground moving target indication (GMTI) applications. First, an adaptive spectrum filtering technique is proposed to compensate the terrain interferometric phase caused by the cross-track baseline and then the ground clutter is rejected by applying the joint-pixel displaced phase center antenna (JPDPCA). After performing the moving target detection, the target radial velocity is estimated according to the azimuth position offset by exploiting the road-aided information. Finally, the along-track baseline is derived based on the subspace projection (SP). The effectiveness of the proposed method is validated by data from the experimental airborne system.

High precision phase-domain radial velocity estimation for wideband radar systems

Radial velocity estimation used in wide-band radar systems is investigated. By analyzing the signal of cross-correlation output of adjacent echoes, it is found that the frequency and phase of the cross-correlation output are related to the target's radial velocity. Since the precision of the phase estimation is higher than that of the frequency, a phase-based velocity estimator is proposed. However, the ambiguity problem exists in the phase estimators, and thus the estimation of the cross-correlation of adjacent echoes (CCAE) is used to calculate the ambiguity number. The root-mean-square-error (RMSE) of the proposed estimator is derived. Simulation results show that the performance of the proposed method is better than that of the frequency-based estimator.

An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES

Abstract The EXtreme-PREcision Spectrograph (EXPRES) is an environmentally stabilized, fiber-fed, R = 137,500, optical spectrograph. It was recently commissioned at the 4.3 m Lowell Discovery Telescope near Flagstaff, Arizona. The spectrograph was designed with a target radial-velocity (RV) precision of 30 cm s−1. In addition to instrumental innovations, the EXPRES pipeline, presented here, is the first on-sky, optical, fiber-fed spectrograph to employ many novel techniques—including an “extended flat” fiber used for wavelength-dependent quantum efficiency characterization of the CCD, a flat-relative optimal extraction algorithm, chromatic barycentric corrections, chromatic calibration offsets, and an ultra-precise laser frequency comb for wavelength calibration. We describe the reduction, calibration, and RV analysis pipeline used for EXPRES and present an example of our current sub-meter-per-second RV measurement precision, which reaches a formal, single-measurement error of 0.3 m s−1 for an observation with a per-pixel signal-to-noise ratio of 250. These velocities yield an orbital solution on the known exoplanet host 51 Peg that matches literature values with a residual rms of 0.895 m s−1.

Space Maneuvering Target Integration Detection and Parameter Estimation for a Spaceborne Radar System With Target Doppler Aliasing

Space maneuvering target detection and parameter estimation are the challenging problems in a spaceborne radar system. The complex motion of an observed target usually leads to the range migration (RM) and Doppler frequency migration, causing the difficulty in target detection. Furthermore, the relative high speed of space maneuvering target and limited pulse repetition frequency will result in Doppler ambiguity, further degrading the target detection performance. In this article, a novel and efficient coherent accumulation algorithm is proposed, which considers the velocity ambiguity and Doppler aliasing caused by the target radial velocity and acceleration, respectively. In the proposed method, the target radial velocity and acceleration are first separated by applying the time reversal transform technique. Then, the target radial velocity is estimated by using the Keystone transform. After compensating the velocity effects, the frequency reversal transform is proposed to remove the residual RM, and the acceleration estimation can be efficiently accomplished by the nonuniform fast Fourier transform. Compared with the conventional coherent integration methods, the proposed method can be suitable for the motion parameter estimation and coherent integration detection for a maneuvering target with velocity ambiguity and spectrum aliasing. Additionally, the proposed method is computationally efficient since only the complex multiplication and fast Fourier transform calculations are involved. Both simulation experiments and measured data results are provided to verify the effectiveness of the proposed algorithm.

EVALUATION OF THE POSSIBILITIES OF PROVIDING THE NECESSARY ACCURACY OF THE RADIAL VELOCITY MEASURING OF A TARGET BY COHERENT-PULSE RADARS OUTSIDE THE LINE OF SIGHT

The purpose of the article. The article estimates the possible values of the components of the mean-square error of measuring the radial velocity of the target which appear as a result of fluctuations of the phase of the radio signal outside the radar line of sight. The expediency of using a coherent burst of radio pulses to provide the necessary detection range with specified quality indicators is substantiated. Consideration is carried out for a model of a signal with a random amplitude and an initial phase. It is assumed that phase fluctuations are distributed according to the normal law with zero mean, and their correlation decreases with an increase in the interval between the radio bursts of the packet alternating. Results. The results show that due to the phase fluctuations of the radio pulses of the received pack, the mean-square measuring error of the target radial velocity can exceed the values determined by the tactical requirements for coherent-pulse radars. Conclusions. The performed numerical analysis allows to determine the degree of reduction of the quality of the radio pulses burst time-frequency processing in coherent-pulse radars and evaluates the degree of reduction of the effectiveness of the further secondary processing of the radar information.

A Robust Radial Velocity Estimation Method for FDA-SAR

In multi-channel synthetic aperture radar-ground moving target indication (SAR-GMTI), most radial velocity estimation methods are based on the phase difference between channels. However, the image coregistration and channel phase errors will have a severe impact on the phase difference between channels. Moreover, it deteriorates the performance of the moving target radial velocity estimation. To solve this problem, a robust radial velocity estimation method is proposed using a frequency diverse array-SAR (FDA-SAR) in this letter. By introducing the step frequency, the interferometric phase among channels is a linear function of the Doppler frequency. The radial velocity of moving targets is embedded in the first-order term of the linear function. Meanwhile, the first-order term does not include channel phase error terms. Therefore, the accurate velocity of moving targets is estimated by the first-order coefficient which is solved by the least-squares fitting method. Afterward, according to the analysis and derivation, the proposed method is robust on the condition of image coregistration error. At last, simulations and data analysis illustrate the effectiveness of the proposed method.

A Scheme for Multitarget Lateral Velocity Measurement With High-Frequency Monostatic Radar

This paper proposes a method for extracting the lateral velocity in multitarget cases to improve the ship tracking capability of high-frequency surface wave radar (HFSWR). The method exploits the phase interferometry between two antenna arrays that is done in the time domain after joint frequency–azimuth filtering. First, a frequency filter based on generalized S transform with a variable factor is applied to eliminate the background noise. The variable factor is linked to the target's radial velocity and can control the time and frequency resolutions. We then use two identical subarrays as two receiving channels to implement the azimuth filtering. Based on adaptive minimum-variance distortionless response beamforming, the extraneous signals can be suppressed. Subsequently, the varying slope of the phase difference of the target of interest signal from two channels can be extracted to compute the lateral velocity in a low signal-to-noise ratio scenario. The interference of noise and extraneous target signals is analyzed using simulations, and the effectiveness of the frequency–azimuth filtering method is validated with both simulations and experimental data. In addition, the high spatial resolution ship tracking results over an hour match well with automatic identification system data, demonstrating the feasibility of tracking targets with HF monostatic radar.

Near‐space hypersonic target coherent integration algorithm based on search compensation

A near-space hypersonic target coherent integration algorithm based on search compensation is proposed for the problem of range gate stride and Doppler extension. The algorithm first estimates the target radial velocity and Doppler rate by searching, and then completes coherent integration of echo signal via distance and phase compensation according to the estimated values. The simulation results show that the algorithm can effectively solve the problem of range gate stride and Doppler extension, suppress noise, and increase gain. The integration effect of the proposed algorithm is obviously superior to the classical moving target detection (MTD) algorithm.

Robust Radial Velocity Estimation Based on Joint-Pixel Normalized Sample Covariance Matrix and Shift Vector for Moving Targets

The clutter suppression and target radial velocity estimation are essential in the ground moving target indication processing with multichannel synthetic aperture radar (SAR) systems. In reality, the heterogeneous clutter, the image coregistration error, and channel mismatch will remarkably decline the estimation performance of the target radial velocity. To address these issues, a robust radial velocity estimation algorithm is proposed in this letter. Based on the joint-pixel signal model, the joint-pixel normalized sample covariance matrix (JPNSCM) is employed to mitigate the effect of heterogeneous clutter, and the shift vector determined by JPNSCM is used to obtain the actual target steering vector. Then, the adaptive matched filtering algorithm is adopted to estimate the target radial velocity. Compared with traditional estimation algorithms, the proposed method obtains better performance in both simulations and real SAR data experiments.

Radar High-Speed Maneuvering Target Detection Based on Three-Dimensional Scaled Transform

This paper presents a novel coherent high-speed maneuvering target detection algorithm, which is based on the three-dimensional (3-D) scaled transform. This algorithm coherently integrates the echo energy into a peak in a 3-D parameter space and estimates the target's radial velocity and acceleration simultaneously by the peak detection technique. Thereafter, compensating off the across range unit and Doppler frequency migration via estimations, this algorithm coherently integrates the echo energy in the range-Doppler space and uses the constant false alarm rate technique to complete the target detection. The cross term of the proposed algorithm is also analyzed and its characteristic indicates the applicability in the scenario of multiple targets. The computational complexity, resolution, peak-to-sidelobe level (PSL), and detection performance are analyzed and compared with several typical algorithms, which leads us to conclude that the proposed algorithm can strike a balance between the computational complexity and detection performance with high resolution and PSL. Finally, experiments with the real measured radar data are conducted to verify the proposed algorithm.

Azimuth Location Deambiguity for SAR Ground Moving Targets via Coprime Adjacent Arrays

The ground moving target's radial velocity estimation based on the interferometric phase in a multichannel synthetic aperture radar (SAR) system suffers from 2π modulo folding, resulting in the target's azimuth location ambiguity in the SAR image. To address this problem, a novel coprime adjacent arrays SAR (CAA-SAR) is proposed in this paper. The two sparse uniform subarrays constituting the CAA are arranged adjacently with a conjunct element, then a virtual array can be obtained with much more virtual elements and smaller element spacing, which will help to solve the azimuth location ambiguity. After ground clutter suppression, multiple pixels’ samplings are utilized based on the MUSIC algorithm for estimating radial velocity as well as azimuth shift by exploiting all virtual elements of CAA-SAR. Compared with the existing nonuniform linear array SAR method based on Chinese remainder theorem, the CAA-SAR can obtain a better accuracy with the same number of elements in a larger sparse configuration, or use fewer elements to obtain an approximate accuracy in almost the same physical aperture. Compared with the coprime arrays SAR, the CAA-SAR has a better accuracy due to its larger number of unique virtual elements and longer physical aperture. Finally, some results of numerical experiments are provided to demonstrate the effectiveness of the proposed method.

Entanglement-enhanced lidars for simultaneous range and velocity measurements

Lidar is a well known optical technology for measuring a target's range and radial velocity. We describe two lidar systems that use entanglement between transmitted signals and retained idlers to obtain significant quantum enhancements in simultaneous measurement of these parameters. The first entanglement-enhanced lidar circumvents the Arthurs-Kelly uncertainty relation for simultaneous measurement of range and radial velocity from detection of a single photon returned from the target. This performance presumes there is no extraneous (background) light, but is robust to the roundtrip loss incurred by the signal photons. The second entanglement-enhanced lidar---which requires a lossless, noiseless environment---realizes Heisenberg-limited accuracies for both its range and radial-velocity measurements, i.e., their root-mean-square estimation errors are both proportional to $1/M$ when $M$ signal photons are transmitted. These two lidars derive their entanglement-based enhancements from use of a unitary transformation that takes a signal-idler photon pair with frequencies $\omega_S$ and $\omega_I$ and converts it to a signal-idler photon pair whose frequencies are $(\omega_S + \omega_I)/2$ and $\omega_S-\omega_I$. Insight into how this transformation provides its benefits is provided through an analogy to superdense coding.

A Tracking algorithm for Super-speed Maneuvering Target Based on Velocity Measurement

To solve the problem of super-speed maneuvering target tracking in the 3D space. An adaptive algorithm for the super-speed tracking using the radial velocity was presented for radar awareness system, which can detect target radial velocity and target angular velocity. Compared with the traditional algorithm for variable structure multiple models (VSMM) in the track of target maneuvering by the simulation analysis. The simulation result shows that this algorithm has more simple structure, higher positioning accuracy and better maneuver detection. The new tracking algorithm has some value for project practice.